The problem with BJJ is that in a pure form, BJJ does not give you a way to "win." You have to control the person and then break something. The problem comes when any of the witnesses recount the story to the police - you put him in a "judo lock" and then broke his arm, even though he had stopped fighting back.

Uhhhh.... If people are watching, how is the woman going to be raped? Are they just sitting by eating popcorn while this rape is going on?

If she gets a control hold on him, she could just yell for help to these bystanders. If they're not helping or there are no bystanders, break the arm, choke him out, whatever. It doesn't matter because she is being raped.